Electron attachment mass spectrometry as a diagnostics for electronegative gases and plasmas

Abstract

. Electron attachment mass spectrometry as a diagnostics for electronegative gases and plasmas. Review of Scientific Instruments, 69(1), 116-122. DOI: 10.1063/1.1148486 General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Electron attachment mass spectrometry ͑EAMS͒ has been developed to study mixtures of electronegative gases and plasmas. A quadrupole mass spectrometer ͑QMS͒ has been used to detect negative ions, formed from sampled species by attachment of low energy electrons. Varying the electron energy allows to collect the attachment cross section of the considered species. EAMS appears to be a very powerful technique to study the chemistry of electronegative gases. Unlike ionization mass spectrometry, where cross sections are low at the threshold and rather flat over a broad range of electron energies, attachment resonances are sharp and distinct. Also very limited fragmentation of the parent negative ion occurs, so a given molecule yields only a few different negative ions. This facilitates identification of components in a gas mixture. It is particularly advantageous for detection of large, fragile molecules, which break up after ionization, but can be easily transformed into large negative ions. Moreover, sensitive detection of active species is possible due to their relatively high attachment cross sections. A particularly important application of EAMS is the determination of an effective attachment cross section in a plasma. Recording this cross section allows to decide on the actual negative ion formation mechanism in the plasma environment, where active products of plasma conversion can significantly alter the negative ion production channels and consequently the whole balance of charged particles. Examples of EAMS applications to fluorocarbon gases and low-pressure radio-frequency plasmas are discussed. In a CF 4 discharge conversion of the parent gas into species like C 2 F 6 and C 3 F 8 is easily visualized. The dominant mechanism of negative ion formation in the plasma is electron attachment to these minority species and not to the parent gas. Also larger polymers are readily formed in fluorocarbon plasmas. In a C 2 F 6 discharge molecules with up to ten carbon atoms ͑the mass limit of our apparatus͒ have been detected using EAMS.

Study of Electronegative Ar/O2 Discharge by Means of Langmuir Probe

“…It is supposed that the dissociative electron attachment, when the oxygen molecule is first dissociated by electron impact and then the negative atomic ion is created by electron attachment, is the main mechanism of generation of negative ions in the plasma. The dissociation energy amounts to 5.1 eV, the resonance electron energy for dissociative attachment is around 6.5 eV [9]. As at the height of 65 mm the average electron energy about 5.4 eV is closest to these values, the production of negative ions is there most intensive.…”

The OES Diagnosis in Removal of HCHO by the Uniform Bipolar Nanosecond-Pulsed DBD Using Wire-Cylinder Electrode Configuration in Atmospheric N2

“…Furthermore, when the proportion of O 2 rises more than 5%, the emission intensity of OH (A 2 → X 2 , 0−0) is nearly zero. In addition, too much O 2 could consume a lot of 5-8-eV energetic electrons by the attachment reaction [37], [38] e + O 2 → O − 2 (25) which would decrease the removal rate of HCHO. Hence, when increasing the proportion of O 2 within 5%-20%, the HCHO removal rate decreases gradually.…”

Production and loss of CF 2 and CF radicals at the polymerization in CF 4 plasma

“…It is reasonable that researches of CF4 plasma attract so particular interest [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. No wonder that many electrodynamic models of CF4 plasma with using different sets of electron scattering cross-sections on CF4 molecules exist now [15][16][17][18][19][20].…”